GenChem 1111: Mid-Term Study Guide

GenChem 1111: Mid-Term Study Guide

Exp 1: Basic Lab Operation and Dry Lab

1. Bunsen Burner Operation

   • Valves and Ignition Order: Proper sequence for opening valves and igniting the burner is crucial to ensure safety and functionality.

   • Air-Control Valve:

     • Description: Adjusts the amount of air entering the burner.

     • Color Changes:

     • Sufficient Air: Blue flame.

     • Insufficient Air: Yellow/orange flame (cool flame).

   • Flame Types:

     • Cool Flame: Low temperature.

     • Hot Flame: High temperature used for various reactions.

2. Density Calculations

   • Formula: $D = \frac{M}{V}$ (Density = Mass/Volume).

   • Unknown Solid:

     • How to measure the volume of an unknown solid is required for density calculation.

     • Effect of Partial Immersion:

     • If the solid does not immerse completely into water, the recorded volume will be lower than the actual volume.

     • This leads to:

       • $D = \frac{M}{V}$

       • If $V$ is measured lower, then $D$ will be overestimated (higher than actual density).

   • Unknown Liquid: Calculation of density and the effect of evaporation must be considered.

3. Reading Volume: Skills for accurately measuring volume using a graduated cylinder.

4. Significant Figures: Importance of following significant figure rules during calculations.

Exp 2: Empirical Formulas

1. Magnesium and Oxygen Reaction

   • Combination Reaction: Characterized by two substances (reactants) combining to form one product.

     • Example Reaction: $2Mg + O_2 \rightarrow 2MgO$

   • Molar Masses:

     • Magnesium (Mg): 24.32 g/mol.

     • Oxygen (O): 16 g/mol.

   • Calculations: Determine the mass of $MgO$ or $O_2$ reacted from given mass of $Mg$.

2. Crucible Usage: Necessary techniques for safely heating magnesium.

3. Dry Agent: Identify agents that change color during reactions, indicating progress or completeness.

4. Concept of Mole:

   • Understand calculations for empirical formulas and mass percentages from experimental data.

   • Balancing Equations: Required for successful calculations in lab reports.

Exp 3: Limiting Reactants

1. Double Displacement Reaction: Example given:

   • $Sr(NO<em>3)</em>2(aq) + 2KIO<em>3(aq) \rightarrow Sr(IO</em>3)<em>2(s) + 2KNO</em>3(aq)$

2. Limiting Reactants: Definition and importance in reactions; identifies which reactant will determine the maximum amount of product produced.

3. Yield Percentage Calculations:

   • Definitions:

     • Theoretical Yield: The calculated max product from complete reaction.

   • Practice Example:

     • For reactions of 1.0 mole $Sr(NO<em>3)</em>2$ with 1.5 moles $KIO_3$:

     • Determine grams of precipitate produced and yield percentage if an actual yield of 280g is achieved.

     • Identification of limiting reactant is essential (1.5 moles $KIO_3$ is limiting).

     • Calculation of $Sr(IO<em>3)</em>2$:

       • Reaction Ratio: 1 mol $Sr(NO<em>3)</em>2$ reacts with 2 moles $KIO_3$

       • Calculation:

       • $x$ moles from limiting reactant gives 0.75 moles

       • Mass Calculation:

         • $0.75 ext{ mol} * 437.4 ext{ g/mol} = 328.1 ext{ g}$.

       • Yield Percentage:

         • $\frac{280}{328.1} * 100\% = 85.3\%$.

4. Example for Li/N2 Reaction:

   • Reaction: $6Li(s) + N<em>2(g) \rightarrow 2Li</em>3N(s)$

   • Molar ratios given align with initial amounts, confirming limiting reactant and resulting product quantity (1 mol of $Li_3N$).

   • Example Mixture:

     • 0.810 g of $BaCl<em>2\cdot2H</em>2O$ and $Na<em>2SO</em>4$ leads to 0.466 g of $BaSO_4$.

   • Calculate mass percentages of components in the original mixture based on theoretical calculations.

     • Ensure to define limiting reactants as necessary in calculations.

Exp 4: Chemistry of Copper

1. Copper (Cu) Properties: Awareness of physical and chemical characteristics crucial in studies.

   • Five reactions observed:

     • Transformation: $Cu \rightarrow Cu(NO<em>3)</em>2 \rightarrow Cu(OH)<em>2 \rightarrow CuO \rightarrow CuSO</em>4 \rightarrow Cu$.

   • Observations regarding color change and state changes important for documenting experiments.

2. Types of Reactions:

   • Definitions and examples of:

     • Double Displacement Reaction.

     • Decomposition Reaction.

     • Oxidation-Reduction (Redox) Reaction.

3. Recovery Percent Calculation.

Exp 5: Chemical Reactions

1. Types of Reactions: Review and understand different reaction types, including:

   • Combination, Decomposition, Single/Double Displacement Reactions.

2. Redox Reactions: Definitions and process understanding:

   • Oxidation Process: Loss of electrons by a substance.

   • Reduction Process: Gain of electrons by a substance.

   • Identification of reducing agent (e.g., Zinc (Zn) as reducing agent) and oxidizing agent (e.g., Copper (Cu) as oxidizing agent).

3. Equations: Know how to write different types of chemical equations:

   • Molecular Equation Example:

     • $CaCl<em>2\cdot2H</em>2O(aq) + K<em>2C</em>2O<em>4\cdot H</em>2O(aq)\rightarrow CaC<em>2O</em>4\cdot H<em>2O(s) + 2KCl(aq) + 2H</em>2O(l)$

   • Complete Ionic Equation:

     • $Ca^{2+}(aq) + 2Cl^{-}(aq) + 2H<em>2O(l) + 2K^{+}(aq) + C</em>2O<em>4^{2-}(aq) + H</em>2O(l)\rightarrow CaC<em>2O</em>4\cdot H<em>2O(s) + 2K^{+}(aq) + 2Cl^{-}(aq) + 2H</em>2O(l)$

   • Net Ionic Equation: Result after removing spectator ions:

     • $Ca^{2+}(aq) + C<em>2O</em>4^{2-}(aq) + H<em>2O(l)\rightarrow CaC</em>2O<em>4\cdot H</em>2O(s)$